Axial dispersion during low Reynolds number Taylor-Couette flow: intra-vortex mixing effects

Tracer experiments were employed to study axial mass transport in a Taylor-Couette device with a radius ratio of 0.875. The inner cylinder was rotated (with the outer cylinder fixed) at circumferential Reynolds numbers ranging from 1.05 to 7.50 times the critical value for the onset of laminar Taylor vortex flow. Apparent axial dispersion coefficients were found by fitting a three parameter model to tracer-response data. The model consisted of a network of CSTRs (each with an associated exchange volume) connected in series. The CSTRs corresponded to the well mixed outer layers of the Taylor vortices; the exchange volumes represented poorly mixed vortex cores. For 1.05 less than or equal to Re/Re-c < 5.0, the apparent axial dispersion coefficient increased nonmonotonically with increasing Reynolds numbers. At inner cylinder rotation rates Re/Re-c > 5.0, the model recovered the commonly used discrete approximation of the one-dimensional diffusion equation. (C) 1997 Elsevier Science Ltd.